Generally speaking, a microelectromechanical system (“MEMS”) is a highly miniaturized device having both electrical and mechanical components. MEMS devices are typically fabricated on or from a substrate material, such as silicon or polysilicon. Various electrical and mechanical structures are formed in the MEMS using a variety of techniques.
The mechanical structures of the MEMS are typically very fragile, and can be easily damaged. Furthermore, the mechanical structures of the MEMS are typically very sensitive, and can be easily impeded. Stiction, which is a surface adhesion force that tends to prevent relative motion between two moveable parts of the MEMS device, can be a particular problem both during device fabrication as well as in use over the lifetime of the device. Various techniques have been used to reduce stiction including coating the MEMS structures with a wafer anti-stiction agent (“WASA”), such as an organic material. For example, U.S. Pat. No. 5,694,740 to Martin et al., which is expressly incorporated by reference herein in its entirety, describes such techniques. Further, U.S. Pat. No. 7,364,942 to Martin, which is expressly incorporated by reference herein in its entirety, also describes such techniques.
Many factors can affect MEMS performance, including dirt, moisture, and even static electricity. Therefore, a cap is typically placed over substantially all of the MEMS mechanical components in order to protect the mechanical components of the MEMS device. The cap typically includes a cavity to allow the MEMS structures to move while simultaneously protecting the structures from the operating ambient. The cap is bonded onto the MEMS in such a way that the MEMS structures to be protected are positioned within the MEMS cavity. This bond is often formed so that the device is hermetically sealed against contaminants.